1. Field of the Invention
The present invention relates to a data communication system, data communication method, data communication apparatus and digital interface, particularly to a network in which information data (including image data) and command data are mixed to perform communication at high speed and a communication protocol applicable to the network.
2. Related Background Art
Hard discs and printers have heretofore had highest frequencies of use among peripheral apparatuses of personal computers (hereinafter referred to as PC). These peripheral apparatuses are connected to PC via dedicated input/output interfaces, SCSI (small computer system interfaces) or other general-purpose digital interfaces.
On the other hand, in recent years, digital cameras, digital video cameras and other AV (Audio/Visual) apparatuses have gained public attention as PC peripheral apparatuses. The AV apparatuses are also connected to PC via dedicated interfaces.
FIG. 1 is a view showing a conventional communication system constituted of PC and AV apparatus.
In FIG. 1, numeral 101 denotes an AV apparatus or digital camera, 102 denotes PC, and 103 denotes a printer.
The digital camera 101 comprises a memory 104 in which a photographed image is compressed and recorded; a decoding unit 105 for expanding and decoding the compressed image data recorded in the memory 104; an image processing unit 106; a D/A converter 107; a display 108 comprising EVF; and a dedicated digital I/O unit 109 for connecting the digital camera 101 and the PC 102.
The PC 102 comprises a dedicated digital I/O unit 110 for connecting the PC 102 and the digital camera 101; an operation unit 111 comprising a keyboard, a mouse and the like; a decoding unit 112 for expanding and decoding the compressed image data; a display 113; a hard disc 114; RAM or another memory 115; an MPU 116; a PCI bus 117; and an SCSI interface 118 for connecting the PC 102 and the printer 103.
The printer 103 comprises an SCSI interface 119 for connecting the printer 103 and PC 102; a memory 120; a printer head 121; a printer controller 122 for controlling operation of the printer 103; and a driver 123.
In the conventional communication system, since the digital interface or digital I/O unit 109 of the digital camera 101 is not compatible with the digital interface or SCSI interface 110 of the printer 103, they cannot be directly interconnected. For example, a still image needs to be transmitted to the printer 103 from the digital camera 101 necessarily via the PC.
Moreover, in the conventional dedicated interface or the SCSI interface, when a large volume of data such as still images or moving images held by the AV apparatus are handled, many problems are caused that a data transfer rate is low, communication cable for parallel communication is thick, there are only a small number of types of connectable peripheral apparatuses, connection system is limited and that real-time data transfer cannot be performed.
Known as one of next-generation high-speed high-performance digital interfaces to solve the problems is an IEEE (The Institute of Electrical and Electronics Engineers, Inc.) 1394-1995 standards.
A digital interface conforming to the IEEE 1394-1995 standards (hereinafter referred to as the 1394 interface) has the following characteristics:
(1) data transfer rate is high;
(2) real-time data transfer system (i.e., Isochronous transfer system) and Asynchronous transfer system are supported;
(3) connection structure (topology) with a high degree of freedom can be constructed; and
(4) plug-and-play function and hot-line plug/unplug function are supported.
In the IEEE 1394-1995 standards, although a physical, electric structure of a connector, two basic data transfer systems, and the like are defined, it is not defined what type of data is transmitted/received based on what communication protocol in what data format.
Moreover, in Isochronous transfer system of the IEEE 1394-1995 standards, since a response to a sending packet is not defined, there is no guarantee that each Isochronous packet is surely received. Therefore, when a plurality of continuous data are to be securely transferred, or when one file data is segmented into a plurality of data to be securely transferred, Isochronous transfer system cannot be used.
Furthermore, in Isochronous transfer system of the IEEE 1394-1995 standards, even when there is a vacancy in a transfer band, the total number of communications is limited to 64. Therefore, when a large number of communications are performed in a little transfer band, Isochronous transfer system cannot be used.
Additionally, in the IEEE 1394-1995 standards, if bus rest occurs in response to the turning ON/OFF of a node power supply, the connection/disconnection of a node, or the like, data transfer has to be interrupted. In the IEEE 1394-1995 standards, however, when the data transfer is interrupted by the bus reset or an error at the time of transmission, it cannot be known what content of data is lost. Furthermore, in order to return once interrupted transfer, a very intricate communication procedure needs to be carried out.
Here, the bus reset indicates a function of automatically performing the recognition of a new topology and the setting of an address (node ID) allotted to each node. Therefore, the plug-and-play function and the hot-line plug/unplug function can be provided in the IEEE 1394-1995 standards.
Moreover, in the communication system conforming to the IEEE 1394-1995 standards, a communication protocol has not been concretely proposed for segmenting into one or more segment data and continuously transferring a relatively large amount of object data (e.g., still image data, graphic data, text data, file data, program data, and the like) which are required to have no real-time properties but have reliability.
Furthermore, in the communication system conforming to the IEEE 1394-1995 standards, a communication protocol has not been either concretely proposed for realizing data communication among a plurality of apparatuses using a communication system in which data is asynchronously broadcast.
An object of the present invention is to solve the aforementioned problems.
Another object of the invention is to provide a technique in which object data requiring no real-time properties can continuously and securely be transferred in a data communication system, data communication method, data communication apparatus and digital interface.
A further object of the invention is to provide a technique in which a time interval between continuously transferred data can be optimized in a data communication system, data communication method, data communication apparatus and digital interface, and unnecessary interruption in a series of data transfer can easily, securely and efficiently be prevented.
A still further object of the invention is to provide a technique which can realize an efficient data communication in such a manner that unnecessarily occurring retry can easily and securely be prevented in a data communication system, data communication method, data communication apparatus and digital interface.
As a preferred embodiment for such objects, the present invention discloses a data communication system comprising: a source node for performing asynchronous communication at least once to transfer data comprising one or more segments; one or more destination nodes for receiving the data transferred from the source node; and a controller for setting a logical connection relationship between the source node and the one or more destination nodes, wherein at least one of the source node and the controller controls a timing for performing the asynchronous communication.
As another preferred embodiment, the present invention discloses a data communication system comprising: a source node for performing broadcast communication at least once to transfer data comprising one or more segments based on a logical connection relationship; and one or more destination nodes for receiving the data transferred from the source node based on the logical connection relationship, wherein the source node controls a timing for performing the broadcast communication.
As another preferred embodiment, the present invention discloses a data communication method comprising steps of: setting a logical connection relationship between a source node and one or more destination nodes; performing asynchronous communication at least once to transfer data comprising one or more segments to the one or more destination nodes; controlling a timing for performing the asynchronous communication; and using the logical connection relationship to receive the data transferred using the asynchronous communication.
As another preferred embodiment, the present invention discloses a data communication method comprising steps of: performing broadcast communication at least once to transfer data comprising one or more segments to one or more destination nodes based on a logical connection relationship; controlling a timing for performing the broadcast communication; and receiving the data transferred from the source node based on the logical connection relationship.
As another preferred embodiment, the present invention discloses a data communication method comprising steps of: packetizing data comprising one or more segments into a plurality of communication packets; and successively transferring the communication packets based on a logical connection relationship set with one or more destination nodes, the communication packets being asynchronously transferred after a predetermined time elapses.
As another preferred embodiment, the present invention discloses a data communication method comprising steps of: receiving communication packets successively transferred from a source node based on a logical connection relationship set with the source node, the communication packets being asynchronously transferred after a predetermined time elapses; and writing data included in the communication packets into a memory space common to other apparatuses.
As another preferred embodiment, the present invention discloses a data communication method comprising steps of: setting a logical connection relationship between a source node and one or more destination nodes; notifying the source node and the one or more destination nodes of a connection ID for identifying the logical connection relationship; and setting in the source node a time interval of communication packets successively transferred based on the logical connection relationship.
As another preferred embodiment, the present invention discloses a data communication apparatus comprising: a unit for packetizing data comprising one or more segments into a plurality of communication packets; and a unit for successively transferring the communication packets based on a logical connection relationship set with one or more destination nodes, wherein the communication packets are asynchronously transferred after a predetermined time elapses.
As another preferred embodiment, the present invention discloses a data communication apparatus comprising: a unit for receiving communication packets successively transferred from a source node based on a logical connection relationship set with the source node; and a unit for writing data included in the communication packets into a memory space common to other apparatuses, wherein the communication packets are asynchronously transferred after a predetermined time elapses.
As another preferred embodiment, the present invention discloses a data communication apparatus comprising: a unit for setting a logical connection relationship between a source node and one or more destination nodes and for setting in the source node a time interval of communication packets successively transferred based on the logical connection relationship; and a unit for notifying the source node and the one or more destination nodes of a connection ID for identifying the logical connection relationship.
As another preferred embodiment, the present invention discloses a digital interface comprising: a unit for packetizing data comprising one or more segments into a plurality of communication packets; and a unit for successively transferring the communication packets based on a logical connection relationship set with one or more destination nodes, wherein the communication packets are asynchronously transferred after a predetermined time elapses.
As another preferred embodiment, the present invention discloses a digital interface comprising: a unit for receiving communication packets successively transferred from a source node based on a logical connection relationship set with the source node; and a unit for writing data included in the communication packets into a memory space common to other apparatuses, wherein the communication packets are asynchronously transferred after a predetermined time elapses.
As still further preferred embodiment, the present invention discloses a digital interface comprising: a unit for setting a logical connection relationship between a source node and one or more destination nodes and for setting in the source node a time interval of communication packets successively transferred based on the logical connection relationship; and a unit for notifying the source node and the one or more destination nodes of a connection ID for identifying the logical connection relationship.
Still other objects of the present invention, and the advantages thereof, will become fully apparent from the following detailed description of the embodiments.